Recycling method for oil tank nitrogen sealing gas and oil gas recovered by oil transportation crane pipe

Abstract

The invention relates to a method for simultaneously recycling nitrogen sealing gas in an oil tank and oil gas recovered by an oil transportation crane pipe, which comprises the following steps of: determining the operation pressure of the nitrogen sealing gas to be 200-1000Pa (all pressures below are gauge pressures), immediately supplementing circulating nitrogen when the pressure of the nitrogen sealing gas in the oil tank is lower than 300Pa, setting the pressure of a circulating nitrogen buffer tank to be 100-200KPa, and controlling the pressure of the nitrogen sealing gas in the circulating nitrogen buffer tank to be 100-200KPa when the pressure of the nitrogen sealing gas in the oil tank is lower than 300Pa. The volume of the buffer tank is correspondingly calculated according to the operation volume of the oil tank, and the calculation method is 1 / 4-1 / 3 of the flow volume per hour; the pressure of nitrogen sealing gas in an oil tank is higher than 800Pa, the nitrogen sealing gas is sent to a buffer tank in front of a first compressor to be called oil-rich circulating nitrogen, the pressure of the buffer tank in front of the first compressor is higher than 200Pa, the first compressor is started, the oil-rich circulating nitrogen is compressed to 300KPa by the first compressor, and gas at the temperature of 60-110 DEG C is sent to an ultrafiltration membrane to separate an oil product; the separated oil product is called as circulating nitrogen, is sent to the heat exchanger to be reheated to the normal temperature, is sent to a circulating nitrogen buffer tank with the pressure of 100-200 KPa, and is sent to an inlet buffer tank of a second compressor when the circulating nitrogen is excessive; a loading arm oil gas collection gas inlet adopts-10 to-100 Pa, collected gas is sent to a buffer tank in front of a second compressor, gas collected by the buffer tank is sent to the second compressor, gas at an outlet of the second compressor is 800 KPa, 90-110 DEG C gas is sent to a nanofiltration membrane to separate oil products, the gas is continuously sent to a heat exchanger, a cooler and a freezing dryer to separate oil products, and then the gas is sent to the heat exchanger to be reheated to normal temperature to be called dry air; the dry air is sent to a PSA nitrogen making device to be separated to obtain 99.9% of 0.6 MPa nitrogen, the total VOC content is lower than 1 mg / Nm < 3 >, the nitrogen is sent to a circulating nitrogen tank, meanwhile, 28-35% of oxygen-enriched gas of 1-10 KPa is obtained, the oxygen-enriched gas is sent to a tail gas combustion device, and after combustion tail gas is qualified, heat is recycled and directly exhausted to the atmosphere.

Description

Technical Field

[0001] The present invention relates to the fields of chemical engineering, energy conservation, and environmental protection, and is a method for effectively reducing nitrogen loss, lowering the energy consumption of compressors, and recovering organic substances. Background Art

[0002] There are different organized emission limits for VOCs in different industries in national standards. For example, the "Emission Standards for Pollutants from Petroleum Refining Industry" (GB31570 - 2015), the "Emission Standards for Pollutants from Petrochemical Industry" (GB31571 - 2015), etc. stipulate the VOC emission concentrations and other requirements for the corresponding industries. The VOC emission limit for newly built enterprises in the petrochemical industry is 80 mg / m³, and for existing enterprises is 120 mg / m³.

[0003] In the refining industry, oil products are usually stored by nitrogen blanketing of storage tanks. Nitrogen is replenished and discharged by controlling the pressure in the storage tank, and the discharged nitrogen contains VOC gases. At the same time, when filling an oil tanker with an oil loading arm, the air in the transport tank is discharged and mixed with the VOC gases in the oil products and recovered. A large amount of oxygen contained therein is likely to form an explosive hazardous environment, and a certain proportion of nitrogen needs to be replenished to dilute it. These two streams of gas generally pass through a cooler at a certain temperature under low pressure to recover liquefied products, and the remaining gas is sent to the flare for combustion and discharged after passing the standards.

[0004] On November 30, 2023, the State Council issued the "Action Plan for Continuous Improvement of Air Quality" (Guo Fa 〔2023〕 No. 24), which clearly requires in the chapter of "VI. Strengthening the reduction of multiple pollutants and effectively reducing the emission intensity" that "enterprises shall not use flare combustion devices as daily air pollution treatment facilities". The main reason for its prohibition as a daily air pollution treatment facility is that although flare combustion can treat combustible gases to a certain extent, it is not the most effective pollution control method and cannot meet the increasingly strict requirements for air pollution prevention and control. Using it as a daily treatment facility may cause some enterprises to neglect the front-end treatment and recycling of waste gases, which is not conducive to reducing pollutant emissions from the source, nor to promoting enterprises to adopt more advanced and environmentally friendly waste gas treatment technologies and equipment to achieve the discharge standards and emission reduction goals of pollutants.

[0005] Zhu Liang et al. announced a nitrogen sealed oil-gas recovery device for oil tanks and its usage method in CN119176347A. The nitrogen sealed oil-gas recovery device for oil tanks includes an oil tank, on which a breathing valve is connected. The nitrogen sealed oil-gas recovery device for oil tanks further includes a balance tank, a pressure tank, a boosting device and a control device. A first nitrogen input pipeline is connected to the breathing valve, and a second nitrogen input pipeline is connected to the balance tank. The control device is electrically connected to the oil tank, the balance tank, the pressure tank and the boosting device respectively. It solves the problems that when the traditional nitrogen seal is used in the existing oil-gas recovery system, the nitrogen content in the oil-gas is relatively high and difficult to process, and when the breathing valve of the oil tank sucks in air, it enters the oil tank, posing a safety hazard. The present invention can reduce the nitrogen in the oil-gas recovered from the oil tank. The recovered oil-gas can be used as fuel gas to achieve the goal of energy conservation. At the same time, it can ensure that the original breathing valve of the oil tank can work normally, keep the breathing valve in a nitrogen environment all the time, and eliminate safety hazards.

[0006] Chen Wenwu et al. announced a VOCs safety recovery system and recovery process for styrene storage tanks in CN110564441A. It includes a first atmospheric pressure styrene storage tank, a second atmospheric pressure styrene storage tank, a first suction cryogenic cooler, a second suction cryogenic cooler, a first suction coolant viewing window and a second suction coolant viewing window. An air suction fan is connected to the exhaust port of the first atmospheric pressure styrene storage tank through a first pipeline. The first suction cryogenic cooler is installed on the first pipeline and is used to cool the mixed gas. Among them, the coolant passes through a second pipeline connected to the first suction cryogenic cooler and is introduced into an underground waste oil tank. The air suction fan is also connected to a steam superheater burner. The styrene and air mixed gas extracted by the air suction fan is introduced into the steam superheater burner for incineration. The present invention can prevent the pollution of the environment caused by the volatilization of styrene gas, ensure the safety and reliability of the recovery process, and hardly consume nitrogen during normal operation. A VOCs recovery system and recovery process for light oil storage tanks announced in CN110562621A is similar to it.

[0007] Gu Jian announced a closed oil tank oil-gas treatment process device in CN109351116A, which successively sets a nitrogen storage tank, the top gas cavity of an oil product storage tank, a condensation system, an incineration device and a chimney according to the gas flow. The nitrogen storage tank provides nitrogen for gas sealing of the top gas cavity. The condensation system has a condensate outlet and a non-condensable gas outlet. The incineration device is used to incinerate the organic matter in the non-condensable gas. There is also an adsorption device between the condensation system and the incineration device to adsorb the adsorbable light hydrocarbon substances in the gas that cannot be condensed. After the incineration device, there is another pipeline connecting to the nitrogen storage tank. In the present invention, N2 and VOCs waste gas are introduced into the oil product storage tank for nitrogen sealing, with a closed cycle, greatly reducing the nitrogen usage. The gas after incineration contains CO2, H2O, unburned O2 and VOC, etc., and it is unreasonable to send it back to the nitrogen storage tank.

[0008] As can be seen from the above, how to reduce the consumption of nitrogen sealing gas in oil storage tanks while treating VOCs is a difficult problem. For industrial enterprises and practitioners in the environmental protection industry, the treatment method for VOC gases is combustion, and the qualified gases are discharged into the atmosphere. This method ignores the front-end treatment and recycling of VOCs and only achieves the purpose of reducing pollutant emissions. In order to reasonably recycle nitrogen sealing gas, reduce the amount of VOCs burned, and reduce VOC emissions, the following method is specifically invented. Summary of the Invention

[0009] A method for the simultaneous resource utilization of nitrogen sealing gas in oil tanks and recovered oil and gas from loading arms. The operating pressure of the nitrogen sealing gas is determined within 200 - 1000 Pa (gauge pressure, and all pressures below are gauge pressures). When the pressure of the nitrogen sealing gas in the oil tank is lower than 300 Pa, circulating nitrogen is immediately supplemented. The pressure of the circulating nitrogen buffer tank is set at 100 - 200 KPa, and the volume of the buffer tank is calculated corresponding to the operating volume of the oil tank. The calculation method is 1 / 4 - 1 / 3 of the hourly flowing volume; when the pressure of the nitrogen sealing gas in the oil tank is higher than 800 Pa, the nitrogen sealing gas is sent to the buffer tank in front of the first compressor, which is called rich oil circulating nitrogen. When the pressure of the buffer tank in front of the first compressor is higher than 200 Pa, the first compressor is started. The first compressor compresses the rich oil circulating nitrogen to 300 KPa, and the gas at 60 - 110 °C is sent to the ultrafiltration membrane to separate the oil products, and then sent to the heat exchanger, cooler, and cold dryer to separate the oil products, which is called circulating nitrogen. Then it is sent to the heat exchanger to be reheated to room temperature and sent to the circulating nitrogen buffer tank at 100 - 200 KPa. When the circulating nitrogen is in excess, it is sent to the buffer tank at the inlet of the second compressor; the inlet of the oil and gas collecting gas of the loading arm adopts -10 - -100 Pa, and the collected gas is sent to the buffer tank in front of the second compressor. The gas collected in the buffer tank is sent to the second compressor. The gas at the outlet of the second compressor is 800 KPa, and the gas at 90 - 110 °C is sent to the nanofiltration membrane to separate the oil products, and then sent to the heat exchanger, cooler, and cold dryer to separate the oil products, and then sent to the heat exchanger to be reheated to room temperature, which is called dry air. The dry air is sent to the PSA nitrogen generation device to separate and obtain 99.9% nitrogen at 0.6 MPa, where the total amount of VOCs is lower than 1 mg / Nm 3 , and it is sent to the circulating nitrogen tank. At the same time, oxygen-rich gas with 1 - 10 KPa and 28 - 35% oxygen is obtained. The oxygen-rich gas is sent to the tail gas combustion device, and after the combustion tail gas is qualified, the heat is recovered and directly discharged into the atmosphere.

[0010] Preferably, the first compressor is a nitrogen compressor, the outlet pressure is higher than 200 KPa, and the outlet gas is sent to the inlet of the second stage of the second compressor.

[0011] Preferably, the second compressor is an air compressor. When the inlet pressure is lower than -100 KPa, the rotation speed of the compressor is reduced to ensure that the outlet pressure reaches 0.8 MPa, and the cycle time of the PSA nitrogen generation is increased in a chain reaction to ensure that the oxygen content in the PSA nitrogen generation is lower than 0.1%.

[0012] Preferably, 1 - 10 KPa of oxygen-rich gas with a concentration of 28 - 35% is used. The oxygen-rich gas is sent to the internal heat cycle of the tail gas combustion device, and the combustion temperature is controlled to be higher than 400 °C, thereby ensuring that the total non-methane hydrocarbons in the discharged atmospheric gas are lower than 30 mg / Nm 3 .

[0013] Preferably, a VOC adsorbent is filled at the bottom of the PSA nitrogen production adsorption tower, and a nitrogen production molecular sieve is filled at the upper part. The oxygen and nitrogen flowing out during the regeneration process of the nitrogen production adsorbent can regenerate the VOC adsorbent simultaneously, and VOC is removed and enters the oxygen-rich gas while producing nitrogen.

[0014] Preferably, 4000 - 6000 mg / Nm of VOC must be retained in the 1 - 10 KPa oxygen-rich gas with a concentration of 28 - 35%. This is achieved by adding a nanofiltration membrane bypass to avoid the need to supplement other fuels due to insufficient heat value to maintain its own heat balance. 3

[0015] Compared with the methods announced in other processes, the present invention has the following characteristics: 1. Nitrogen is basically fully recycled, and only a very small amount of nitrogen needs to be replenished to maintain the system balance; 2. When the recycled nitrogen is in excess, it is sent to the second compressor, and the amount of nitrogen is controlled by the PSA nitrogen production device, reducing the waste caused by nitrogen emissions. At the same time, the compressor load is adjustable to adapt to the change in the nitrogen filling amount of the oil truck; 3. The gas collected by the loading crane pipe is recovered and collected; 4. VOC is separated while producing nitrogen by PSA; 5. Supplementary fuel is not required for the catalytic combustion of VOC; 6. The formation of a deflagration dangerous environment is avoided throughout the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 is a simplified process flow diagram of the present invention. EMBODIMENTS

[0017] Example 1. A method for simultaneously recycling and resource utilization of nitrogen sealing gas in an oil tank and recovered oil and gas from an oil loading arm. The operating pressure of the nitrogen sealing gas is 600 Pa. When the nitrogen sealing gas pressure in the oil tank is 830 Pa, a part of the nitrogen sealing gas is discharged and sent to the buffer tank in front of the first compressor. The pressure of the buffer tank in front of the first compressor is 270 Pa. The first compressor is started. The rich oil circulating nitrogen gas pressure at the outlet of the first compressor is 0.3 MPa and the temperature is 60 °C. The gas is sent to the ultrafiltration membrane to separate the liquid, and then sent to the heat exchanger, cooler, and cold dryer to separate the oil products. After that, it is heated to 25 °C through the heat exchanger and sent to the circulating nitrogen buffer tank; the inlet of the oil and gas collection gas of the oil loading arm is -10 Pa, which is sent to the buffer tank in front of the second compressor. Part of the air is supplemented into the buffer tank, and the outlet gas is sent to the second compressor together. The gas pressure at the outlet of the compressor is 0.8 MPa, and the outlet gas at 98 °C is sent to the nanofiltration membrane to separate the oil products. Then it is continuously sent to the heat exchanger, cooler, and cold dryer to separate the liquid, and then heated to 25 °C through the heat exchanger. The gas is dry air containing VOC. The dry air is sent to the PSA nitrogen generation device to separate and obtain 0.6 MPa nitrogen with a purity of 99.9%, where the VOC content is 0.5 mg / Nm 3 , the O2 content is 0.05%, and the nitrogen gas is sent to the circulating nitrogen gas tank. At the same time, a gas of 8 KPa is obtained, in which the oxygen concentration is 31% and the VOC concentration is 4655 mg / Nm 3 , which is sent to the tail gas combustion device. The combustion tail gas is qualified and directly discharged to the atmosphere after heat exchange.

[0018] Example 2. A method for simultaneously recycling and resource utilization of nitrogen sealing gas in an oil tank and recovered oil and gas from an oil loading arm. The operating pressure of the nitrogen sealing gas is 662 Pa. When the nitrogen sealing gas pressure in the oil tank is 850 Pa, a part of the nitrogen sealing gas is discharged and sent to the buffer tank in front of the first compressor. The pressure of the buffer tank in front of the first compressor is 300 Pa. The first compressor is started. The rich oil circulating nitrogen gas pressure at the outlet of the first compressor is 0.3 MPa and the temperature is 63 °C. The gas is sent to the ultrafiltration membrane to separate the liquid, and then sent to the heat exchanger, cooler, and cold dryer to separate the oil products. After that, it is heated to 26 °C through the heat exchanger and sent to the circulating nitrogen buffer tank. At this time, the amount of circulating nitrogen gas is excessive, and part of the nitrogen gas is sent to the second compressor; the inlet of the oil and gas collection gas of the oil loading arm is -17 Pa, which is sent to the buffer tank in front of the second compressor. The amount of air supplemented into the buffer tank is reduced, and the outlet gas and the circulating nitrogen gas are sent to the second compressor together. The gas pressure at the outlet of the compressor is 0.8 MPa, and the outlet gas at 105 °C is sent to the nanofiltration membrane to separate the oil products. Then it is continuously sent to the heat exchanger, cooler, and cold dryer to separate the liquid, and then heated to 27 °C through the heat exchanger. The gas is dry air containing VOC. The dry air is sent to the PSA nitrogen generation device to separate and obtain 0.6 MPa nitrogen with a purity of 99.9%, where the VOC content is 0.8 mg / Nm 3 , the O2 content is 0.07%, and the nitrogen gas is sent to the circulating nitrogen gas tank. At the same time, a gas of 6 KPa is obtained, in which the oxygen concentration is 29% and the VOC concentration is 5236 mg / Nm 3 , which is sent to the tail gas combustion device. The combustion tail gas is qualified and directly discharged to the atmosphere after heat exchange.

[0019] Example 3. A method for simultaneously recycling and resourceifying the nitrogen sealing gas of an oil tank and the recovered oil vapor of an oil loading arm. The operating pressure of the nitrogen sealing gas is 580 Pa. When the pressure of the nitrogen sealing gas in the oil tank is 810 Pa, a part of the nitrogen sealing gas is discharged and sent to the buffer tank in front of the first compressor. The pressure of the buffer tank in front of the first compressor is 300 Pa. The first compressor is started. The pressure of the rich oil circulating nitrogen at the outlet of the first compressor is 0.3 MPa and the temperature is 65 °C. The gas is sent to an ultrafiltration membrane to separate the liquid, and then sent to a heat exchanger, a cooler, and a cold dryer to separate the oil products. After that, it is heated to 26 °C through the heat exchanger and sent to the circulating nitrogen buffer tank. The inlet of the oil loading arm oil vapor collection gas is -112 Pa, which is sent to the buffer tank in front of the second compressor. The air supplement in the buffer tank is reduced. The outlet gas and the circulating nitrogen are sent to the second compressor together. The gas at the outlet of the compressor is 0.8 MPa and the outlet gas temperature is 101 °C, which is sent to a nanofiltration membrane to separate the oil products, and then continues to be sent to a heat exchanger, a cooler, and a cold dryer to separate the liquid. After being heated to 26 °C through the heat exchanger again, the gas is dry air containing VOCs. The dry air is sent to a PSA nitrogen generation device to increase the cycle time of the PSA device, and nitrogen with a purity of 99.9% and a pressure of 0.6 MPa is separated, where the VOC content is 0.8 mg / Nm 3 , the O2 content is 0.08%, and the nitrogen is sent to the circulating nitrogen tank. At the same time, a gas with a pressure of 6 KPa is obtained, in which the oxygen concentration is 32% and the VOC concentration is 4875 mg / Nm 3 , which is sent to the tail gas combustion device. After the combustion of the tail gas is qualified, it is directly discharged to the atmosphere after heat exchange.

Claims

1. Method for simultaneously recycling oil tank nitrogen sealing gas and recovered oil gas of oil delivery pipe, characterized in that The operating pressure of the nitrogen sealing gas is determined within 200 - 1000 Pa (gauge pressure, and all pressures below are gauge pressures). When the nitrogen sealing gas pressure of the oil tank is lower than 300 Pa, circulating nitrogen is immediately supplemented. The pressure of the circulating nitrogen buffer tank is set at 100 - 200 KPa, and the volume of the buffer tank is calculated corresponding to the operating volume of the oil tank. The calculation method is 1 / 4 - 1 / 3 of the hourly flowing volume; when the nitrogen sealing gas pressure of the oil tank is higher than 800 Pa, the nitrogen sealing gas is sent to the buffer tank in front of the first compressor and is called rich oil circulating nitrogen. When the pressure of the buffer tank in front of the first compressor is higher than 200 Pa, the first compressor is started. The first compressor compresses the rich oil circulating nitrogen to 300 KPa, and the gas at 60 - 110 °C is sent to the ultrafiltration membrane to separate the oil products, and then continues to be sent to the heat exchanger, cooler, and cold dryer to separate the oil products, which is called circulating nitrogen. Then it is sent to the heat exchanger to be reheated to room temperature and sent to the circulating nitrogen buffer tank at 100 - 200 KPa. When the circulating nitrogen is excessive, it is sent to the buffer tank at the inlet of the second compressor; the inlet of the loading arm oil and gas collecting gas uses -10 - -100 Pa, and the collecting gas is sent to the buffer tank in front of the second compressor. The gas collected in the buffer tank is sent to the second compressor. The gas at the outlet of the second compressor is 800 KPa, and the gas at 90 - 110 °C is sent to the nanofiltration membrane to separate the oil products, and then continues to be sent to the heat exchanger, cooler, and cold dryer to separate the oil products, and then sent to the heat exchanger to be reheated to room temperature, which is called dry air. The dry air is sent to the PSA nitrogen generation device to separate and obtain 99.9% nitrogen at 0.6 MPa, where the total VOC content is lower than 1 mg / Nm 3 , and is sent to the circulating nitrogen tank. At the same time, 1 - 10 KPa, 28 - 35% oxygen-rich gas is obtained. The oxygen-rich gas is sent to the tail gas combustion device, and after the combustion tail gas is qualified, the heat is recovered and directly discharged to the atmosphere.

2. The first compressor described in claim 1 is a nitrogen compressor, with an outlet pressure higher than 200 KPa, and the outlet gas is sent to the inlet of the second stage of the second compressor.

3. The second compressor described in claim 1 is an air compressor. If the inlet pressure is lower than -100 KPa, the rotational speed of the compressor is reduced to ensure that the outlet pressure reaches 0.8 MPa, and the cycle time of PSA nitrogen production is increased through interlock to ensure that the oxygen content in PSA nitrogen production is lower than 0.1%.

4. The oxygen-rich gas of 1-10 KPa and 28-35% as described in claim 1 is sent to the tail gas combustion device for internal heat circulation, and the combustion temperature is controlled to be higher than 400 °C, thereby ensuring that the total non-methane hydrocarbons in the exhausted atmospheric gas are lower than 30 mg / Nm 3 .

5. The bottom of the PSA nitrogen adsorption tower described in claim 1 is filled with VOC adsorbent, and the upper part is filled with nitrogen molecular sieve for nitrogen production. The oxygen and nitrogen flowing out during the regeneration process of the nitrogen production adsorbent can regenerate the VOC adsorbent simultaneously, and VOC is removed while producing nitrogen and enters the oxygen-rich gas.

6. In the oxygen-enriched gas of 1-10 KPa and 28-35% described in claim 1, it is necessary to retain 4000-6000 mg / Nm 3 VOC. This purpose is achieved by adding a nanofiltration membrane bypass to avoid the need to supplement other fuels due to insufficient calorific value to maintain its own heat balance.

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